1. Field of the Invention
The present invention is directed toward an efficient spatial image separator, and in particular, to a signal processing apparatus that separates and selectively recombines segments of an image pattern, redirecting composite beams onto photodetector elements.
2. Background
There are numerous optical applications that require efficient processing of complex image patterns. For example, optical phase measurement processors are known which accept signals from an antenna pair, and measure the electrical phase difference. For example, U.S. Pat. No. 5,682,238 to Levitt et al. (the subject matter of which is incorporated herein by reference) discloses a signal processing apparatus that provides phase difference measurements of multiple signal inputs. FIG. 1 depicts one embodiment of such a channelized phase detector. Conceptually, a coherent laser source 24 is split into two optical beams 26, 26' each illuminating an Bragg Cell optical modulator 27, 29 whose RF inputs contain a relative phase difference to be measured. The two RF-modulated optical beams interfere spatially along the phase axis at the Fourier plane. (Optical beam deflection also occurs along an orthogonal axis proportional to input frequency, but is irrelevant for the purposes of this discussion). The resultant optical interference pattern is modulated by a gaussian envelope as shown in FIG. 2. To measure spatial phase of the interference pattern, three photodetectors, D1, D2 and D3, sample within a single period of the pattern. (In the figure, photodetector placement is depicted by rectangular blocks shown directly above the pattern for reference.) However, accurate phase measurements can only be achieved under conditions of minimum envelope rolloff across the sampling region, hence the arrangement of FIG. 2 produces unacceptable results. This is because the gaussian apodization envelope distorts object spatial phase information contained in the optical interference pattern within. FIGS. 3a and 3b show one conventional approach to this problem with the interference period to gaussian envelope width relationship being controlled through design parameter changes. In this configuration, a narrow central region of the interference pattern is utilized to minimize phase measurement errors due to envelope roll-off. This will reduce signal measurement errors associated with envelope apodization, allowing for a spatially accurate signal intensity transfer. Also apparent in FIG. 3b is the low energy utilization because the photodetector capture area is a small fraction of the entire beam envelope; less than 8 percent in one actual implementation. However, reduced energy at the photodetectors disadvantageously results in a loss of system sensitivity, due to decreased signal-to-noise ratio at the photodetector outputs.
Thus, there is a need for a signal processing arrangement that will reserve information content of an image pattern, while significantly improving energy utilization.